1. Field of the Invention
The present invention is directed to a novel communications apparatus that scrambles data to be communicated in order to prevent unauthorized use of the data in wired or wireless communications. The present invention is also directed to an arrangement in which a single host computer synchronizes a plurality of terminals in transfer timing when the plurality of terminals send data in wired communications using wired line.
2. Description of the Prior Art
Thanks to advanced data transmission technology, we can enjoy communications between personal computers in an easy manner over public telephone line or dedicated line. Radio digital signal transmission technology has now matured enough to allow PCM communications to be in widespread use.
When data to be communicated is open to the public free of charge, no consideration is given to secrecy requirements of the data. Thus, the data is not subjected to any particular maneuver for this requirement; attaching a packet number and an error correction code onto the data to be communicated may be sufficient.
Since information is gaining more and more significance in today's information environment, data that requires protection are increasing accordingly. Conventionally, data to be communicated is coded by an encoder prior to transmission. A receiver has a decoder that decodes encoded data which the receiver has received. The encoding and decoding are performed according to a predetermined communication protocol.
The encoder for encoding data to be communicated has a cryptographic program for encoding the data according to predetermined sequence. Once decoded, however, the data are accumulated in a normal state. The user of a terminal may pay for a first use of the data. For subsequent use, however, the data may be available to the user free of charge. This allows practically unauthorized use, and presents a serious problem to an information provider at a host computer side. Such a system presents no problem if the data is of such a nature that it is at the user's disposal at the terminal once the host computer downloads the data to the terminal. Depending on the type of data, the information provider may want to bill the user for each service, that is, the downloading of the data. If the data is stored at the terminal, however, no subsequent service is requested, and thus no billing occurs.
In data communications, the data transmission rate is also an issue. A limitation is imposed on the data transmission rate, particularly a wired network such as wired telephone line. The data transmission rate is also dependent on the modem or interface that connects the terminal with the line. Varied transmission rates are available from a number of modems. Assuming that two computers having respective modems are linked and that one modem has a higher transmission rate than the other, the lower transmission rate overrides.
Thus, communications take place between the two computers at the lower transmission rate rather than at the higher transmission rate if one modem is faster than the other. In the system where a plurality of terminals are connected, via respective modems, to a host computer that is capable of accommodating a plurality of telephone lines, the host computer processes data on a task by task basis, and does not synchronize to the lowest transmission rate. In this case, the data rate of each terminal's modem determines the communications rate between the host computer and each terminal. The data transmission rate of the host computer is thus varied from terminal to terminal. This arrangement presents no problem in a system wherein each terminal accesses information from the host computer that stores some particular database. Other type of systems may be contemplated. For example, a plurality of terminals simultaneously access a host computer, and the host computer has to process sequentially a plurality of commands from the terminals. In such a system, the decision of data transmission rate cannot be left to the responsibility of each modem. To exemplify this, consider that a host computer stores a video game that may be simultaneously played by a plurality of terminals. Varied data transmission rates among the terminals present a problem. Terminals computers can participate in the video game which is controlled by the host computer, but input timing may be critical in enjoying a video game, particularly ones like shooting games. Differences in data rates biases some participants in their favor at the expense of others who are trying to enjoy the video game. Although the input timing of the command, that is the participant's direct responsibility is a major factor, the difference in data transmission rates among modems contributes to biased conditions of the game.